Apparatus for cracking and burning hydrocarbons



July1,1969 A; WERNEL ET AL 3,453,084

APPARATUS FOR CRACKING AND BURNING HYDROCARBONS Filed April 18, 1966 US. Cl. 23277 2 Claims ABSTRACT OF THE DISCLOSURE Apparatus for cracking and burning hydrocarbons so as to produce incandescent carbon particles comprises a mixing chamber from which a flammable mixture strikes a baflie member behind which the burning gases recirculate. The hydrocarbons are injected through the bafflemember into the recirculating gases where they are cracked.

Many processes for cracking gaseous hydrocarbons are already known, and particularly for cracking natural gas in the industrial burners intended for thermal assemblies, apart'from processes which make use of double combustionl In these processes, it is attempted to obtain a raising of thegas temperature, so as to permit the said gas to crack partially before burning in order to liberate particles of free carbon, thus increasing the luminosity of the flames during the subsequent combustion. Nevertheless, in these processes, the flames obtained in the combustion of the pre-cracked gas do not have a very satisfactory luminosity, since the carbon which is formed can only be transported with difliculty and the major part thereof remains on the walls of the reactor. The use of fluidised or catalytic beds does not enable the problem to be resolved, because the free carbon remains on the particles forming the beds.

Moreover, it is known that in order to obtain high outlet velocities of flames of hydrocarbons and particularly of natural gas at the mouth of the burner, it is necessary to stabilise the flames, either by a mechanical device forming a deflector which sets up downstream a stable zone of recycled gases, or by a pilot flame.

The present invention is concerned with an arrangement for the cracking and combustion of hydrocarbons, particularly natural gas, which comprises at the outlet end of the burner a mechanical stabilising member such as a disc, cylinder or the like, which creates downstream a stable zone of recycled gases, the said arrangement being characterised in that it comprises means permitting the introduction of fuels to be burnt within the stabilised recirculation zone.

The introduction means are formed by a secondary pipe opening at the centre of the mechanical stabilisation member, thus supplying a part of the fuel downstream of the mechanical stabilising member.

The fuel to be burnt inside the stabilised recirculation zone can be supplied either in gaseous form or in liquid form.

The fuel to be burnt within the stabilised recirculation zone can either be the same gaseous fuel as the main fuel, adapted to burn in the pre-mixing chamber, or another fuel less volatile than the gaseous one.

This means that the secondary pipe opening at the centre of the metal stabilising member can either be a pipe independent of the main supply pipe for the stream of gas to be burnt in the premixing chamber, or a secondary pipe connected to this main pipe.

United States Patent The interest of this arrangement in the case where liquid fuel is used is to be able to provide a considerable thermal efficiency with a partial supply of liquid petroleum without requiring a vaporiser on the liquid supply.

This arrangement has an even greater interest in the case of butane, because of the fact that it can be used in liquid phase and thus all the difliculties normally inherent in the nature of this gas are obviated; namely, vaporizing and maintaining a gaseous phase in the pipes.

Finally, injecting the hydrocarbon in liquid form into the zone of the hot gases recycled downstream of the stabilizer avoids the frosting effect which is due to the evaporation of the liquid hydrocarbon.

The outlet opening of the secondary circuit is adapted to the nature of the fuel being used; the dimensions thereof can vary over a wide range from the minimum orifice permitting the passage of a hydrocarbon in the liquid state.

The proportions of the flow of gaseous fuel for the primary flame and of the liquid or gaseous fuel flow of the secondary jet are regulated so as to obtain the desired flame length and luminosity.

A number of examples of burners according to the invention and the types of supply arrangements which can be used with these burners are indicated below.

The burner shown diagrammatically in FIGURE 1 is a device known as being of the primary pre-mixing type, with separate injection of primary and secondary fuels.

The burner shown diagrammatically in FIGURE 2 is a primary pre-mixing device with single fuel supply.

The burner shown in FIGURE 3 is a device known as the injection type with separate supply of primary and secondary fuels.

The burner shown in FIGURE 4 is an injection-type device with single fuel supply.

The cracking and combustion arrangement shown in FIGURE 1 comprises a pre-mixing chamber 1, into which extends a supply pipe 2 for the gaseous primary fuel and a supply pipe 3 for injected combustion supporter. A secondary fuel supply pipe 4 arranged parallel to the premixing chamber 1 opens at the centre of a disc 5 which is formed with a central hole 6 and is disposed at the outlet from the pre-mixing chamber 1.

The gaseous primary fuel and the combustion supporter, mixed in the pre-mixing chamber, burn normally at the mouth of the burner, giving a stabilised primary flame 7. The secondary fuel jet discharging through the stabiliser hole 6 is in contact with the burnt gases of the primary flame where it is vaporised and partially dissociated, and then cracked.

The arrangement operates as follows: a part of the fuel is introduced into the pre-mixing chamber, where it is mixed with a combustion supporter, as for example air, the said combustion supporter being introduced into the pre-mixing chamber through the pipe 3.

The part of the fuel introduced into the chamber is mixed with the combustion supporter in proportions which are substantially stoichiometric proportions, or in proportions such that the mixture is slightly oxidising.

This mixture burns normally, giving a stabilised flame which will be referred to as the primary flame. The other part of the flow of the gaseous fuel, which generally constitutes the major part, is introduced through the pipe downstream of the stabiliser into the zone of recycled gases.

This fuel jet, which will be referred to as the secondary jet, is in intimate contact with the burnt gases originating from the primary flame; it is brought to a suflicient temperature and under adequate chemical conditions to ensure partial dissociation and the cracking thereof, so as to liberate particles of free carbon, and as a result to obtain after the recirculation zone a flame which has a high luminosity.

In the arrangement for cracking gaseous hydrocarbons 4 temperatures T and also the monochromatic emission factor were measured with a thickness of flame of about 0.4 metre.

Fuel Supply of fuel Diameters in mm.

TE Emission Primary Secondary Primary Secondary 1 9 C.) fact or Nat. gas Nat. gas Nmfi/h--- 55 Nmfi/h.-- 90 63 14 1, 330 0. D do 5 N111. /h- 55 Nmfi/h.-. 90 63 14 1,300 2 Propane gas 14 kg./h. 26 kg./h 55 38 8 1, 380 0. 4 Liquid propane 5 kg./h kg./h 35 25 2 1, 350 0. 3

in accordance with the present invention, the primary mix- 15 The cracking arrangement according to the invention ture is ignited at the periphery of the stabiliser and sets up downstream of the latter a zone of recycled hot gases; the secondary jet reaches this zone, where it is heated and brought to the conditions for cracking, it being possible for this jet to be initially at ambient temperature or preheated.

It is well to point out that a gradient exists between the temperature at which the jet is introduced into the recirculation zone of the gases and the final temperature of the flame, which can be between 1000 C. and 1800 (1, depending on the conditions under which the secondary air is supplied (pressure, temperature, etc.) and also the conditions of operation.

A flame of high luminosity is obtained after the recirculation zone established by a stabiliser.

For example, the following results were obtained with a burner having a pre-mixing chamber with a diameter of 35 mm., the stabiliser disc positioned at the outlet end of this chamber having a diameter of 25 mm. and the hole formed in the centre of the stabiliser disc being 2 mm.; the supply of gaseous primary fuel of the propane gas type was 5 kg./h., the supply of secondary fuel of the liquid propane type was 35 kg./h. and the air for combustion was at ambient temperature.

A temperature of monochromatic brilliance T of 13S0 and a monochromatic emission factor of 0.32, measured with a flame having a thickness of about 0.4 metre, were noted.

The burner shown in FIGURE 2 is a modification of the burner shown in FIGURE 1, which comprises a single fuel supply pipe 8 instead of two separate pipes, a branch pipe 9 thereon for carrying the fluid to the centre of the stabiliser 10.

The burner shown in FIGURE 3 is a modification of the burner according in FIGURE 1, which comprises an injector arrangement instead of the pre-mixing arrangement; the primary mixture is obtained in the pre-mixing chamber 11 by intake of air 12, this resulting from the suction due to the presence of an injector 13 at the discharge end of the gaseous fuel supply pipe 14. The remainder of the burner is similar to that previously described.

The burner shown in FIGURE 4 is a modification of the burners shown in FIGURES 2 and 3.

The primary mixture is obtained in the pre-mixing chamber 15 by intake of air 16, the suction effect being due to the presence of an injector 17 at the outlet end of the gaseous fuel supply pipe 18. A branch pipe 19 on the said pipe 18 takes up the fluid in order to lead it into the centre of the stabiliser 20.

For example, We have obtained the following results with different hydrocarbons; the air for combustion was at ambient temperature and the monochromatic brilliance has numerous advantages and in particular the operation of this arrangement is very economical, since firstly it does not require any external assistance, whether catalytic or as regards energy, and secondly it uses air as the combustion supporter.

The arrangement according to the invention permits at the same time relatively high gas discharge velocities and strong flames without requiring other stabilising devices.

Another advantage consists in the fact that the arrangement according to the invention is extremely simple in construction and as a consequence does not require any special machining.

It is obvious that the invention is not limited to the constructional examples described above and that it would be possible to visualise other modification without thereby departing from the scope of the invention.

What we claim is:

1. Apparatus for cracking and burning hydrocarbons, comprising supply means for fuel gas and for combustion supporting gas, a mixing chamber for said fuel gas and said com-bustion supporting gas, said chamber having a circular outlet opening for the discharge of the mixture, a circular baflie member in unitary assembly with the mixing chamber but disposed outside said chamber coaxial with and beyond said outlet opening in the direction of discharge of said mixture from said outlet opening, said baflle member having one side which faces said outlet opening, the diameter of said baffle member being less than the diameter of said outlet opening whereby said mixture leaving said outlet opening subsequently passes about the edges of said bafiie member and recycles toward said baflie member, and conduit means extending centrally through said baffle member for conveying said hydrocarbons to the other side of said baflle member in the central zone of said baffle member and for discharging said hydrocarbons in the same direction as the direction of discharge of said mixture from said outlet opening but in the direction opposite the direction of said recycling gas.

2. Apparatus as claimed in claim 1, in which said baffle member is a flat disc.

References Cited UNITED STATES PATENTS 3,290,120 12/1966 Wright et al 23-259.5 3,222,131 12/1965 Powell et a1 23--209.4 3,060,003 10/ 1962 Williams 23209.4 3,009,787 11/1961 Ruble 23--259.5

JAMES H. TAYMAN, IR., Primary Examiner.

US. Cl. X.R. 

